JP2018176195A - Side guide member for hot-rolling factory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a side guide member for hot-rolling factories equipped with a cladding-by-welding layer excellent in matrix hardness, abrasion resistance and crack resistance on the surface of a substrate.SOLUTION: There is provided a side guide member for hot-rolling factories in which a cladding-by-welding layer having a metal matrix in which Cr, Mo, V, Si, Co and Nb solid-solve in an Fe group, a first carbide, a second carbide with inevitable impurities is formed on a surface. In the side guide member, the area ratio of the first carbide to the cladding-by-welding layer is 0.3% or more but 1.5% or less, and the second carbide comprises an added NbC having a grain size of more than 50 μm and a deposited NbC having the grain size of 50 μm or less. The area ratio of the second carbide to the above layer is 25% or more; that of the added NbC to the layer is 16% or more; and that of the deposited NbC to the layer is 1.0% or more. Besides, the sum of the area ratios of the deposited NbC and the first carbide to the layer is 8.0% or less.SELECTED DRAWING: None

Description

  The present invention relates to a hot-rolling mill side guide member provided with a buildup weld layer excellent in wear resistance and crack resistance on the surface of a base material.

  The side guide liners and side guide rollers used in the hot rolling plant apply pressure from the width direction to the steel strip after hot rolling so that the steel plate does not deviate from the correct winding position when winding the steel strip. At this time, since the steel strip contacts with the side guide liner and the side guide roller at high speed, the side guide liner and the side guide roller are exposed to the severe wear environment. Therefore, high abrasion resistance is required for the side guide liners and the side guide rollers.

  In addition, since the side guide liner and the side guide roller are used under an environment where temperature changes rapidly, cracks may develop from the surface layer of the weld overlay due to thermal fatigue and may be missed starting from this crack portion.

  Various patent documents have been disclosed as methods for solving the above problems. In Patent Document 1, the basic composition of the deposited steel metal is C: 0.5 to 1.5%, Si: 0.2 to 2.0%, Mn: 0.3 to 6.0%, Cr: 0 .3 to 10.0%, Co: 0.3 to 10.0%, the balance Fe, and further, one or more selected from V, Ni, Mo, W, Al, and Cu. A welding material is disclosed.

  However, even if the hardfacing weld material described in Patent Document 1 is welded to the side guide liner, sufficient wear resistance can not be obtained. In addition, although it is disclosed to precipitate carbide of Cr for the purpose of improving wear resistance, since this Cr carbide precipitates linearly at grain boundaries, the cracking sensitivity is enhanced and the welding steel starts cracking. There is a risk of missing.

  Patent Document 2 discloses a build-up weld layer in which a mixed powder containing at least one or more of NbC powder, VC powder, and TiC powder is dispersed in a matrix. However, the main component of the matrix of the weld overlay welding layer is Al, and when Al is used as the matrix, sufficient hardness can not be obtained, and as a result, sufficient wear resistance can not be obtained.

  In Patent Document 3, C: 0.05 to 0.12%, Si: 0.2 to 0.8%, Mn: 0.5 to 1.5%, Cr: 1.0 to 5.0%, Mo: containing 0.1 to 2.0%, Ni: 0.5 to 3.0%, V: 0.1 to 1.0%, Co: 0.5 to 3.0%, W: A build-up welding material is disclosed which contains one or more of 0.1 to 1.0% and the balance is Fe and unavoidable impurities.

  However, the marking material is a welding method by submerged arc welding, and in submerged arc welding, it is difficult to obtain a predetermined welded steel component because penetration is deep, and carbides can not be dispersed. Although it has been shown that fine carbides are dispersed to improve wear resistance, it is difficult to obtain sufficient wear resistance only with the precipitated fine carbides.

  In Patent Document 4, C: 0.5 to 3.0%, Si: 0.2 to 2.0%, Mn: 0.2 to 2.0%, V: 0.5 to 10.0%, Cr : 3.0 to 10.0%, and further Mo: 2.0 to 10.0% and W: 2.0 to 10.0% or both, and the balance is Fe and It discloses a continuous casting method comprising unavoidable impurities. However, in this method, although it is possible to regenerate the rolling composite roll at low cost, it is not possible to obtain a uniform thickness due to bending, dents and oxidation. In addition, heat treatment at a high temperature is required to remove casting stress, and tempering must be performed once or twice at 500 ° C. or more and 600 ° C. or less to make the Shore hardness 70 to 100, etc. , Requires a large number of steps.

  Patent Document 5 discloses a material in which a powder of niobium carbide having an average particle diameter of less than 45 μm is dispersedly added to a Hastelloy-based alloy. Dispersion of niobium carbide is expected to improve wear resistance, but it is considered that the matrix is preferentially worn away because the matrix metal is a Hastelloy alloy and does not have sufficient hardness. . In addition, only niobium carbides having a particle diameter of less than 45 μm have a large matrix area ratio in contact with the wear partner material, and sufficient dispersion resistance can not be obtained without dispersing and adding niobium carbides having a particle diameter of 45 μm or more.

Unexamined-Japanese-Patent No. 6-15481 Japanese Patent Application Laid-Open No. 58-179569 JP 2004-82201 A JP 2012-110968 A JP, 2015-224385, A

  An object of the present invention is to provide a hot rolling mill side guide member provided with a buildup welding layer excellent in matrix hardness, wear resistance and crack resistance on a substrate surface.

  In order to solve the above problems, the hot-rolling factory side guide member having excellent wear resistance and cracking resistance according to the present invention comprises (1) solid solution of Cr, Mo, V, Si, Co and Nb in Fe group And a first carbide of at least one of molybdenum carbide, vanadium carbide and chromium carbide dispersed in the metal matrix, and a second carbide of niobium carbide dispersed in the metal matrix A hot-rolled mill side guide member having a weld overlay formed on the surface thereof, the area ratio of the first carbide to the weld overlay being 0.3% or more. The second carbide is 1.5% or less, and the second carbide is composed of an added NbC having a particle diameter of more than 50 μm and a precipitated NbC having a particle diameter of 50 μm or less, and the second carbide for the overlay welding layer The area ratio is at least 25% or more, the area ratio of the added NbC to the cladding layer is at least 16%, and the area ratio of the precipitated NbC to the cladding layer is at least 1.0 % Or more, and the sum of the area ratio of the precipitated NbC and the first carbide with respect to the weld overlay is 8.0% or less.

  (2) In the configuration of the above (1), C may be in solid solution in the metal matrix.

  (3) In the configuration of the above (2), the area ratio of the second carbide to the weld overlay may be 45% or less.

  (4) In the configuration of the above (3), the cladding layer is, by mass%, C: 0.5 to 2.5%, Si: 0.1 to 1.0%, Cr: 4.0 to 6.0%, Mo: 1.0 to 2.5%, V: 1.0 to 2.5%, Co: 0.5 to 1.5%, Nb: 10.0 to 15.0%, the balance It consists of Fe and unavoidable impurities.

  According to the present invention, it is possible to provide a hot-rolled mill side guide member provided with a buildup weld layer excellent in matrix hardness, wear resistance and crack resistance on the surface of a base material.

  The present invention is applied to a side guide member used in a hot rolling plant. The side guide members include side guide liners and side guide rollers. The side guide liner is used in a hot rolling facility that draws a slab heated to about 1250 ° C. to form a strip steel (hot coil), and has a function of guiding a hot coil conveyed at high speed in a high speed state. ing. In addition, the side guide liners are used in a rapidly changing environment.

  Therefore, it is necessary to protect the surface of the side guide liner with a built-up weld layer that combines excellent wear resistance and cracking resistance. Similarly, the surface of the side guide roller also needs to be protected by a built-up weld layer that combines excellent wear resistance and cracking resistance. In this embodiment, a metal matrix in which Cr, Mo, V, Si and Nb are solid-solved in Fe base, and molybdenum carbide, vanadium carbide and chromium carbide dispersed in the metal matrix are used as a weld overlay of this kind. Among them, the first carbide of at least one type, the second carbide of niobium carbide (hereinafter abbreviated as NbC) dispersed in a metal matrix, and the inevitable impurities are used.

  Here, the above-mentioned build-up welding layer is mass%, C: 0.5 to 2.5%, Si: 0.1 to 1.0%, Cr: 4.0 to 6.0%, Mo: 1.0 to 2.5%, V: 1.0 to 2.5%, Co: 0.5 to 1.5%, Nb: 10.0 to 15.0%, the balance being Fe and unavoidable impurities It is obtained by welding a weld overlay material. In the following description, “%” means “mass%” unless otherwise specified.

  PTA welding is used for the welding method. Here, in submerged arc welding different from PTA welding, it is difficult to obtain a predetermined welded steel component because of deep penetration, and NbC can not be dispersed.

  Cr is in solid solution in the metal matrix which is the welding steel, and improves the strength of the welding steel. Therefore, Cr needs to be added at least 4.0% or more. However, when added in large amounts, it combines with carbon and chromium carbides tend to precipitate at grain boundaries. Since this chromium carbide has a brittle structure, it reduces the crack resistance of the weld overlay. Therefore, the addition amount of Cr should be 6.0% or less.

  Mo is solid-solved in the metal matrix which is welding steel, and improves the strength of the welding steel. Further, by combining with carbon, molybdenum carbide is formed, and the wear resistance of the weld overlay is improved. Therefore, it is necessary to add Mo at least 1.0% or more. However, when added in large amounts, molybdenum carbide is excessively precipitated at grain boundaries, leading to a decrease in crack resistance. Therefore, the addition amount of Mo should be 2.5% or less.

  V dissolves in the metal matrix which is the welding steel, and improves the strength of the welding steel. Further, by combining with carbon, vanadium carbide is formed to improve the wear resistance of the weld overlay. Therefore, V needs to be added at least 1.0% or more. However, when added in large amounts, vanadium carbide is excessively precipitated at grain boundaries, leading to a decrease in crack resistance. Therefore, the amount of V added should be 2.5% or less.

  As described above, it is necessary to limit the amount of precipitation of chromium carbide, molybdenum carbide and vanadium carbide, since excessive precipitation thereof leads to a reduction in crack resistance. Specifically, by limiting the addition amounts of Cr, Mo and V added to the weld overlay material to 6.0% or less, 2.5% or less, and 2.5% or less, respectively, for the weld overlay The area ratio of the first carbide is limited to 1.5% or less.

  Here, the first carbide is made of at least one of chromium carbide, molybdenum carbide and vanadium carbide. In some cases, all of these carbides precipitate, or in some cases, only some of the carbides precipitate, which depends on the amounts of Cr, Mo and V added.

  However, since chromium carbide, molybdenum carbide and vanadium carbide contribute to the improvement of the wear resistance, the area ratio of the first carbide to the weld overlay should be 0.3% or more.

  Co contributes to the improvement of the elongation, squeeze, corrosion resistance, toughness and hardness of the deposited steel, but the addition of a large amount reduces the thermal crack resistance. Therefore, the addition amount range is set to 0.5 to 1.5%.

  Although Si has the purpose of improving corrosion resistance, since a high temperature crack occurs in the weld overlay due to the addition of a large amount, the addition amount range is made 0.1 to 1.0%.

  The buildup welding materials contain 10.0 to 15.0% of Nb, and there are two types of Nb contained in the state of single metal and in the state of carbide. That is, the overlay welding material contains a single metal made of Nb and a carbide made of NbC. When welding a build-up welding material, a part of Nb as a single metal dissolves in a metal matrix which is a welding steel and contributes to the improvement of the strength of the welding steel. Further, the remaining Nb receives a heat at the time of welding to cause a compound reaction with C in the metal matrix, and precipitates as NbC.

  On the other hand, NbC contained in the overlay welding material is dispersed in the metal matrix as it is. In the following description, NbC deposited at the time of welding is defined as deposited NbC, and NbC contained in the build-up welding material before welding is defined as added NbC.

  That is, in the metal matrix, different added NbC and precipitated NbC derived from generation are dispersed, and the wear resistance of the weld overlay is dramatically improved by these added NbC and precipitated NbC.

  The area ratio of NbC to the weld overlay is 25% or more, preferably 30% or more. The area ratio can be determined by image analysis from the result of observation with a scanning electron microscope after mirror polishing the surface of the weld overlay.

  When the area ratio of NbC is less than 25%, the wear resistance of the weld overlay is not sufficient. Here, it is important not only to increase the area ratio of NbC to 25% or more, but also to form NbC contained in the weld overlay by both added NbC and precipitated NbC. When the ratio of a single metal to the Nb contained in the weld overlay material becomes excessively high, it combines with carbon in the matrix to form a large amount of precipitated NbC, and the hardness of the matrix is significantly reduced.

  On the other hand, when the ratio of added NbC to Nb contained in the weld overlay material becomes excessively high, carbides of Cr, Mo and V precipitate at grain boundaries and the like, and the cracking resistance of the metal matrix is significantly reduced. That is, when Nb as a single metal is contained in the weld overlay material, carbon in the weld overlay material reacts preferentially with Nb to form NbC, so carbides of Cr, Mo and V It becomes difficult to precipitate in grain boundaries and the like.

  In short, precipitation NbC is necessary to suppress the elution of the first carbides at grain boundaries, and added NbC is necessary to suppress the decrease in hardness of the matrix due to excessive precipitation NbC. is there. In the present invention, by using two NbCs having different generation mechanisms, both crack resistance and wear resistance are provided.

  From the above reasons, the area ratio of added NbC to the weld overlay should be at least 16% or more, and the area ratio of precipitated NbC should be at least 1.0% or more. The particle size of precipitated NbC is 50 μm or less, and the particle size of added NbC is more than 50 μm.

  Since the precipitated NbC precipitates in a short time when receiving heat during welding, the particle size is smaller than that of the added NbC. In order to set the particle size of precipitated NbC to 50 μm or less, it is preferable to set the particle size of Nb as a single metal contained in the buildup welding material to 45 μm to 250 μm.

  The upper limit value of the area ratio of NbC is not particularly limited, but preferably 45% or less. When the area ratio of NbC is increased to more than 45%, C dissolved in the metal matrix is reduced to cause a decrease in hardness. Preferably, excessive deposition of the first carbide can be suppressed by limiting the content of C contained in the weld overlay material to 2.5% or less.

  On the other hand, when the amount of C added is too small, the precipitated NbC decreases, and the wear resistance can not be obtained. Further, chromium carbide, molybdenum carbide and vanadium carbide also contribute to the improvement of the wear resistance, and therefore, it is necessary to precipitate them so as not to cause a decrease in the crack resistance.

  Therefore, the content of C is preferably 0.5% or more. By setting the content of C to 0.5% or more, the area ratio of the first carbide consisting of at least one of chromium carbide, molybdenum carbide and vanadium carbide to the weld overlay of 0.3% or more Be enhanced.

  The sum of the area ratio of the first carbide to the weld overlay and the area ratio of the precipitated NbC (hereinafter referred to as the total area ratio) should be 8.0% or less. When the total area ratio exceeds 8.0%, carbon in the matrix is excessively reduced and the hardness of the matrix is reduced.

  Next, the present invention will be more specifically described by way of examples. Overlay welding materials having the compositions shown in No. 1 to No. 16 in Table 1 were overlay-welded on the test piece to evaluate crack resistance, wear resistance, and matrix hardness. As a welding method, PTA welding was used.

(Abrasion resistance test)
The test piece is heated to 250 ° C. and fixed, and it is reciprocated 30 times with a hard mating material applied with a load of 5 kg pressed from above. The wear resistance was evaluated by measuring the wear depth at this time. When the wear depth at this time was 30 μm or less, the wear resistance was evaluated as “very good” as being very good. When the wear depth was 31 to 60 μm, the wear resistance was evaluated as "good" as being generally good. When the wear depth was 61 μm or more, the wear resistance was evaluated as "poor" as being poor.

(About crack resistance test)
The test piece was heated for 30 minutes in an electric furnace, and then immersed in water for quenching. The electric furnace temperature was carried out at 500 ° C., 600 ° C. and 650 ° C. Electric furnace heating and quenching were repeated 10 times each from the low temperature region side of the same test piece.

  After the test, PT inspection (penetration flaw inspection) investigated the presence or absence of the crack, and those which did not generate the crack at the time of 500 ° C × 10 times and 600 ° C × 10 times finish had a very good resistance to cracking. Very good. Although cracking did not occur at 500 ° C. × 10 times, when cracking occurred at a temperature range of 600 ° C., the cracking resistance was evaluated as “good” as being generally good. When cracking occurred in a temperature range of 500 ° C., the cracking resistance was evaluated as “poor” as being poor. In addition, PT inspection (penetration flaw inspection) is a kind of nondestructive inspection method, a penetrant is applied to a wound opened on the surface to make it penetrate, and the wound is absorbed by the permeated liquid to enlarge the wound. Test to make it easy to find

(About matrix hardness)
The matrix hardness is measured at 10 points using a micro Vickers hardness tester (load: 0.3 kg) and the average hardness is calculated. As a result, when the Vickers hardness Hv is 600 or more, the matrix hardness is very good. It evaluated by "very good." When the Vickers hardness Hv was 500 to 599, the matrix hardness was evaluated as "good" as generally good.

  When the Vickers hardness Hv was 499 or less, the matrix hardness was evaluated as "poor" as being poor. The micro Vickers hardness tester means that a square indenter diamond indenter is pushed into the surface of the sample (test piece) and the test force is released, and then the diagonal length of the depression left on the surface is measured, and the obtained diagonal It is an apparatus which calculates Vickers hardness using the hollow surface area calculated | required from length, and the said test force.

  If at least one of the crack resistance, the wear resistance, and the hardness of the matrix is evaluated as "poor", the overall evaluation is "poor" as "poor". In the case where the evaluation of at least one of the crack resistance, the abrasion resistance and the hardness of the matrix is "good" and the evaluation of "poor" is not given, the overall evaluation is regarded as "good". When the evaluations of the crack resistance, the abrasion resistance and the hardness of the matrix were all "very good", the overall evaluation was made "very good" as being very good.

  Sample No. In No. 1, the area ratio of precipitated NbC is less than 1.0%, the area ratio of the first carbide is more than 1.5%, and the first carbide is excessively precipitated, so that the evaluation of the crack resistance is “poor "Became. In addition, since the total area ratio of the precipitated NbC and the first carbide was very close to the upper limit of 8%, the evaluation of the matrix hardness was "good". Sample No. In No. 2, the C in the matrix was largely deprived by the precipitated NbC, and the area ratio of the first carbide decreased to less than 0.3%, so the evaluation of the wear resistance became "poor". Also, for sample no. In 2, since the total area ratio of the precipitated NbC and the first carbide was more than 8%, the evaluation of the matrix hardness became "poor".

  Sample No. In No. 3, since the area ratio of the second carbide (NbC) was less than 25%, the evaluation of the wear resistance was "poor". Sample No. In No. 4, since the total area ratio of precipitated NbC and the first carbide is more than 8% and the area ratio of added NbC is less than 16%, the evaluation of the matrix hardness was "poor". Also, for sample no. In No. 4, since the area ratio of the first carbide was less than 0.3%, the evaluation of wear resistance was "poor". Sample No. In No. 5, the evaluation of the matrix hardness was "poor" because the total area ratio of the precipitated NbC and the first carbide is more than 8%.

Claims (4)

A metal matrix in which Cr, Mo, V, Si, Co and Nb are solid-solved in Fe group,
A first carbide dispersed in the metal matrix, the first carbide comprising at least one of molybdenum carbide, vanadium carbide and chromium carbide;
A second carbide of niobium carbide dispersed in the metal matrix;
With unavoidable impurities,
A hot-rolled mill side guide member having a weld overlay formed on the surface,
The area ratio of the first carbide to the weld overlay is 0.3% or more and 1.5% or less,
The second carbide comprises an added NbC having a particle size of more than 50 μm and a precipitated NbC having a particle size of 50 μm or less,
The area ratio of the second carbide to the weld overlay is at least 25% or more,
The area ratio of the added NbC to the weld overlay is at least 16%,
The area ratio of the precipitated NbC to the weld overlay is at least 1.0% or more,
A hot-rolled mill side guide member excellent in wear resistance and cracking resistance characterized in that the sum of the area ratio of the precipitated NbC and the first carbide with respect to the weld overlay is 8.0% or less. .   The hot-rolled mill side guide member excellent in wear resistance and crack resistance according to claim 1, wherein C is solid-solved in the metal matrix.   The hot-rolled mill side guide member excellent in wear resistance and crack resistance according to claim 2, wherein an area ratio of the second carbide to the build-up welded layer is 45% or less. The overlay welding layer is in mass%,
C: 0.5 to 2.5%,
Si: 0.1 to 1.0%,
Cr: 4.0 to 6.0%,
Mo: 1.0 to 2.5%,
V: 1.0 to 2.5%,
Co: 0.5 to 1.5%,
Nb: 10.0 to 15.0%,
The hot-rolled mill side guide member excellent in wear resistance and crack resistance according to claim 3, characterized in that it consists of the balance Fe and unavoidable impurities.